Automatic call transfer system capable of carrying out call transfer without manual operation

ABSTRACT

In an automatic call transfer system for use in carrying out transfer of a terminating call from one of telephone sets (T) to another through an exchange (11), a person identification number (ID) is assigned to each of persons movable in a limited area and is generated from a transmitter (TX) conveyed by each person. The limited area is divided into a plurality of zones (Z) which are defined by receivers (RX) connected through subscriber lines to the exchange, respectively, and which include at least one of the telephone sets, respectively. The person identification number is produced from a transmitter (TX) conveyed by each person and is received by a selected one of the receivers in the zone for the selected receiver to be sent through one of the subscriber lines (L) to the exchange. A line number of the one subscriber line is memorized in a memory of the exchange in correspondence to the person identification number and is changed as each person moves in the limited area. Responsive to the terminating call carrying the person identification number, the exchange searches the memory to detect the line number memorized therein and to transfer the terminating call to one of the telephone sets indicated by the memorized line number.

BACKGROUND OF THE INVENTION

This invention relates to an automatic call transfer system for use incarrying out automatic transfer of a call by the use of an exchange.

A recent development of an electronic technique enables realization ofvarious additional functions in the field of telephone exchange.Automatic transfer of a terminating call is known as one of suchadditional functions and serves to automatically transfer theterminating call in a limited area from a certain telephone set toanother one by tracing a destination.

A conventional automatic call transfer system has been used wherein adestination directory number is manually registered into an exchange bya person when he leaves a seat assigned to him.

Another conventional system carries out automatic call transfer by theuse of an automatic dialing set. With this system, a destinationdirectory number is manually set by each person into the automaticdialing set and each call for the person in question is automaticallytransferred through a transfer line to a destination telephone assignedwith the destination directory number.

At any rate, a manual operation should be carried out to set thedestination directory number each time on occurrence of requests oftransfer and is therefore troublesome for each person.

In addition, a person should have a destination directory number changedby any other person when moves among a plurality of differentdestinations or changes a destination on the midway. No change of thedestination directory number results in wrong transfer of a call.

When a single directory number is used in common to a plurality ofpersons, inconvenience takes place such that a busy time becomes long.Furthermore, the transfer operation is carried out irrespective of anemergent call or a nonemergent one.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an automatic call transfersystem wherein no manual operation is necessary on carrying out transferof a call.

It is another object of this invention to provide an automatic calltransfer system of the type described, which can trace a destinationdirectory number even when a person happens to move to a differentdestination, changing an initial destination on the midway to thedifferent destination.

It is still another object of this invention to provide an automaticcall transfer system of the type described, wherein inconvenience doesnot take place even when a telephone set is used in common to aplurality of persons.

It is yet another object of this invention to provide an automatic calltransfer system of the type described, wherein transfer of a call can berequested by a particular person alone to prevent a nonemergent callfrom being transferred.

An automatic call transfer system to which this invention is applicableis for use in automatically carrying out call transfer by the use of anexchange which is coupled through subscriber lines to telephone sets,respectively. The telephone sets are specified by line numberscorresponding to the subscriber lines, respectively, and are distributedin an area so as to be utilized by persons movable in the area.According to this invention, a person identification number is assignedto each of specific ones of the persons so as to identify each specificperson. The system comprises a plurality of receiving means coupled tothe exchange and having receivable zones into which the area is dividedso that at least one of the telephone sets is included in each of thereceivable zones. Each of the receiving means is for receiving anidentification number signal representative of the person identificationnumber. The system further comprises signal generating means conveyed byeach specific person for generating the identification number signalsuch that it is received by a selected one of the receiving means wheneach specific person is staying in the receivable zone for the selectedone of said receiving means. The exchange comprises memory means coupledto the receivers for memorizing specific at least one of the linenumbers of the receivable zone for the selected one of the receivingmeans in correspondence to the identification number signal and calltransferring means coupled to the memory means and responsive to thecall carrying the person identification number for transferring the callto the telephone set specified by the specific at least one of the linenumbers with reference to the memorized identification number signal.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic block diagram of an automatic call transfer systemaccording to a first embodiment of this invention;

FIG. 2 is a time chart for use in describing operation of a radiotransmitter illustrated in FIG. 1;

FIG. 3 is a block diagram of an exchange for use in the automatic calltransfer system illustrated in FIG. 1;

FIG. 4 is a flow chart for use in describing operation of thetransmitter, the exchange, and a receiver which are all illustrated inFIG. 1;

FIG. 5 is a flow chart for use in describing another operation of theexchange illustrated in FIG. 3;

FIG. 6 depicted below FIG. 2, is a time chart for use in describingoperation of an automatic call transfer system according to a secondembodiment of this invention;

FIG. 7 is a block diagram of a radio transmitter for use in theautomatic call transfer system illustrated in conjunction with FIG. 6;and

FIG. 8 is a block diagram of a radio receiver operable in cooperationwith the radio transmitter illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an automatic call transfer system according to afirst embodiment of this invention is for use in carrying out automaticcall transfer by the use of an exchange 11 which will be described laterand which may, for example, be a private branch exchange. Theillustrated system comprises a plurality of telephone sets T₁₀, T₁₁,T₂₀, T₂₁, and T₃₀ distributed in a limited area of an office, a factory,or the like. The telephone sets T (suffixes omitted) are coupled to theexchange 11 through subscriber lines L₁₀, L₁₁, L₂₁, L₂₂, and L₃₀,respectively, and assigned with directory numbers TEL corresponding toline numbers LN₁₀, LN₁₁, LN₂₁, LN₂₂, and LN₃₀ of the subscriber linesL₁₀ through L₃₀, respectively.

It is assumed that each of the telephone sets T is assigned or dispensedto a single person A, B, C, D, or E, and disposed at his seat, althoughit is usable by any other persons and that specific ones A, D, and E ofthe persons are given first through third person identification numbersID₁, ID₂, and ID₃ peculiar thereto. The persons A, D, and E will benamed first, second, and third persons, respectively. Each of thepersons A to E is assumed to free to move in the area.

In the example being illustrated, the area is divided into first throughthird zones Z₁, Z₂, and Z₃ which are determined by first through thirdradio receivers RX₁, RX₂, and RX₃, respectively. The first through thirdzones may partially be intersected to each other. The first throughthird radio receivers RX₁, RX₂, and RX₃ are disposed at center portionsof the first through third zones Z₁, Z₂, and Z₃, respectively, and areconnected to the exchange 11 through selected ones L₁₀, L₂₀, and L₃₀ ofthe subscriber lines of the first through third zones Z₁ to Z₃. Inasmuchas the selected subscriber lines L₁₀, L₂₀, and L₃₀ are also connected tothe telephone sets T₁₀, T₂₀, and T₃₀, the first through third radioreceivers RX₁, RX₂, and RX₃ are connected to the selected subscriberlines L₁₀, L₂₀, and L₃₀ in parallel to the telephone sets T₁₀, T₂₀, andT₃₀. From this fact, it is readily understood that the area is dividedso that at least one of the telephone sets is placed in each of thefirst through third zones Z₁, Z₂, and Z₃.

The line numbers LN₁₀, LN₂₀, and LN₃₀ for the selected subscriber linesL₁₀, L₂₀, and L₃₀ may be called first, second, and third line numbers,respectively.

The first through third persons A, D, and E are possessed of firstthrough third portable radio transmitters TX₁, TX₂, and TX₃ (will simplybe called radio transmitters) which generate, as radio signals, firstthrough third identification number signals representative of the firstthrough third person identification numbers ID₁ to ID₃, respectively.Each radio signal may be of an ultra high frequency band and is producedby the portable radio transmitters TX with electric power of, forexample, 0.1 milliwatt.

Temporarily referring to FIG. 2, the portable radio transmitters TX areassumed to be equal in number to n in FIG. 2 and produce the given orassigned identification number signals (ID) as successions of firstthrough n-th bursts, respectively. For example, the first portable radiotransmitter TX₁ produces the first bursts having a first period t₁, asillustrated along a top line TX₁ of FIG. 2. Each of the first burstscarries the first identification number signal (ID₁) The second portableradio transmitter TX₂ produces the second bursts appearing in a secondperiod t₂ which is different from the first period t₁. Like each of thefirst bursts, each of the second bursts conveys the secondidentification number signal (ID₂). Likewise, the n-th bursts have ann-th period t_(n) inherent to the n-th bursts and carry an n-thidentification number signal (ID_(n)).

Thus, the burst successions have different periods from one another inconsideration of collision among the identification number signals (ID)in a single one of the zones Z. For example, a plurality of the burstsuccessions illustrated in FIG. 2 collide with one another at a timeinstant t₀. When the collision takes place in the same zone Z₁, Z₂, orZ₃, each radio receiver RX₁, RX₂, or RX₃ can not receive and reproduceany identification number signals ID. However, the collision isdissolved when the next following burst is received because of thedifferent periods of the burst successions.

Turning back to FIG. 1, each of the first through third identificationnumber signals (ID₁) to (ID₃) can be received by the first through thirdreceivers RX₁ to RX₃ in the first through third zones Z₁ to Z₃. In thissense, each of the first through third zones Z₁ to Z₃ may be called areceivable zone for the radio signals, namely, the first through thirdidentification number signals (ID₁) to (ID₃). Practically, each of thefirst through third zones Z₁ to Z₃ may have a radius between 5 metersand 10 meters in consideration of the electric power of the firstthrough third radio transmitters TX₁ to TX₃. This implies that the radioreceivers may be spaced with a distance of 10-20 meters lefttherebetween.

With this system, the radio receivers RX transfer the personidentification numbers ID (suffix omitted) as electric identificationsignals to the exchange 11 through the first through third subscriberlines L₁₀, L₂₀, and L₃₀ in response to the radio signals carrying thefirst through third identification signals.

Referring to FIG. 3 together with FIG. 1, the illustrated exchange 11accommodates the subscriber lines L (suffixes omitted) clustered into aplurality of groups G₁, G₂, and G₃ which are distributed to differentones of the receivable zones Z. Let the groups G₁, G₂, and G₃ includethe subscriber lines L₁₀, L₁₁ ; L₂₀, L₂₁ ; and L₃₀ (FIG. 1) connected tothe telephone sets of the first through third zones Z₁ to Z₃,respectively. The exchange 11 also accommodates a plurality of externallines EXT, such as main wires, connected to another exchange or thelike.

As is known in the art, the exchange 11 comprises a central control unit(CC) 21 and a switch or link unit 22 operable under control of thecentral control unit 21 to connect or disconnect the subscriber lines L,the external lines, and the like.

In FIG. 3, the exchange 11 further comprises a subscriber memory 25 fortemporarily memorizing status of each subscriber. The illustratedsubscriber memory 25 is connected to the central control unit 21 and theswitch unit 22 through buses and has a line number (LN) area 26 and anidentification (ID) memory area 27. The line number area 26 has firstlocal addresses which correspond to the line numbers LN, respectively,and which are loaded in a known manner with electric signals necessaryfor the exchange 11. The identification memory area 27 has second localaddresses which correspond to the person identification numbers ID,respectively, and each of which is loaded with the line numbers LNassigned to the subscriber lines L. Each line number LN in theidentification memory area 27 specifies a neighboring one of thesubscriber lines, namely, telephone sets near to each person. Thus, theperson identification numbers ID are made to correspond to the linenumbers in the identification memory area 27. It is therefore possibleto detect each position of the specific persons by searching theidentification memory area 27 by the use of the person identificationnumbers ID and by reading the line numbers LN out of the identificationnumber area 27.

The illustrated exchange 11 further comprises an identification numberreceiver (ID REC) 31 for receiving the identification number signals(ID) and first and second talkie units or trunks, namely, audio responseunits or trunks TK₁ and TK₂ which are operable in a manner to bedescribed later.

Referring to FIG. 4 together with FIGS. 1 through 3, operation of thesystem will be exemplified in connection with the first person A whichis given the first identification number ID₁ and his seat in the firstzone Z₁, as illustrated in FIG. 1. The first zone Z₁ may be called ahome zone for the first person A. The first person A always has thefirst radio transmitter TX₁ with him either in his pocket or otherwise.The first identification number ID₁ is generated in the manner describedwith reference to FIG. 2 by the first radio transmitter TX₁ as the radiosignal, as illustrated at a transmitter step TS₁ in FIG. 4.

The radio signal representative of the first identification number ID₁is received by the first radio receiver RX₁ placed in the first zone Z₁as long as the first person A is present in his own seat, as shown at afirst receiver step RS₁ in FIG. 4. As previously mentioned inconjunction with FIG. 2, the first identification number ID₁ is carriedby each burst intermittently appearing at the first period t₁. Onreception of the first identification number ID₁ only one time, thefirst person A in question may happen to merely pass by and may not bestaying in the first zone Z₁.

In order to confirm stay of the first person A in the first zone Z₁, thefirst radio receiver RX₁ monitors whether or not the firstidentification number ID₁ is consecutively received twice or more, asshown at a second receiver step RS₂ in FIG. 4. When the firstidentification number ID₁ is successively received plural times, thesecond step RS₂ proceeds to a third receiver step RS₃. Otherwise, thesecond receiver step RS₂ returns back to the first step RS₁.

At the third receiver step RS₃, the first radio receiver RX₁ judgeswhether or not the first identification number ID₁ was alreadyregistered in the first radio receiver RX₁. If the first identificationnumber ID₁ is not registered in the first radio receiver RX₁ yet, thefirst radio receiver RX₁ registers the first identification number ID₁at a fourth receiver step RS₄ through the subscriber line L₁₀.

When the first identification number ID₁ was already registered in thefirst radio receiver RX₁, the first radio receiver RX₁ must monitorwhether or not the registered number, namely, the first identificationnumber ID₁ is to be erased or released from the exchange 11 because thefirst person A may move from the first zone Z₁ to another one. For thispurpose, the first radio receiver RX₁ supervises lapse of a firstpredetermined duration T₁ by the use of a timer (not shown) at a fifthreceiver step RS₅. The first predetermined duration T₁ may be, forexample, one minute.

After lapse of the predetermined duration T₁, the fifth receiver stepRS₅ is followed by a sixth receiver step RS₆ at which the receiver RX₁judges whether or not the first identification number ID₁ is beingreceived by the first radio receiver RX₁. On reception of the firstidentification number ID₁, the sixth receiver step RS₆ returns back tothe first receiver step RS₁. Otherwise, the sixth receiver step RS₆ isfollowed by a seventh receiver step RS₇ at which the first radioreceiver RX₁ sends the exchange 11 an erasure signal indicative oferasure of the registered, namely, first identification number.

In FIG. 4, the exchange 11 is put into a standby or waiting state at afirst exchange step ES₁ for awaiting reception of any electricidentification number signals representative of the personidentification numbers ID. At a second exchange step ES₂ following thefirst exchange step ES₁, the exchange 11 receives the firstidentification number ID₁ at the identification number receiver (ID REC)31 (FIG. 3) thereof. The central control unit 21 is operated at a thirdexchange step ES₃ in a known manner to detect the line number of thesubscriber line through which the first identification number ID₁ isreceived. In the example being illustrated, the line number LN₁₀ of thesubscriber line L₁₀ is detected by the central control unit 21.

After detection of the line number LN₁₀, the central control unit 21detects whether or not the received identification number, namely, ID₁is sent from the home zone Z₁, as shown at a fourth exchange step ES₄.If the first identification number ID₁ is sent from the home zone Z₁,the central control unit 21 accesses the identification memory area 27(FIG. 3) at a fifth exchange step ES₅ to memorize the line number LN₁₀in a specific one of the second memory addresses that is assigned to thefirst identification number ID₁. Thus, the line number LN₁₀ for thefirst person A is memorized in the identification number memory 27 incorrespondence to the first identification number ID₁ for the firstperson A as long as he is staying in the first or home zone Z₁.

On the other hand, when the first identification number ID₁ is not sentfrom the first or home zone Z₁, the specific address for the firstidentification number ID₁ is loaded at a sixth exchange step ES₆ with aselected one of the line numbers which are assigned to each of theremaining zones, namely, the second or the third zones Z₂ or Z₃. Theselected line number may be, for example, a pilot number of each zone.In the example being illustrated, the line numbers LN₂₀ and LN₃₀ arememorized in the specific address for the first identification numberID₁ when the first person A is staying in the second and the third zonesZ₂ and Z₃, respectively.

At a seventh exchange step ES₇, the central control unit 21 judgeswhether or not the erasure signal is sent from the first radio receiverRX₁ to erase contents of the specific address which are related to thefirst identification number ID₁. Responsive to the erasure signal, thecentral control unit 21 erases the contents of the specific address, asshown at an eighth exchange step ES₈.

The erasure signal is produced either during a short absence of thefirst person A or during his long absence. During the short absence, thefirst person A may be in course of moving from one zone to another.During the long absence, the first person A is probably absent from thelimited area. Under the circumstances, registration is made at a ninthexchange step ES₉ in the specific address for the first identificationnumber ID₁ to indicate that the first person A is in course of movement.After the registration, the central control unit 21 times a secondpredetermined duration T₂ of, for example, five minutes at a tenthexchange step ES₁₀.

Lapse of the second predetermined duration T₂ may regard the firstperson A as absent from the limited area. In the example, the centralcontrol unit 21 detects presence or absence of a request forregistration related to the first identification number ID₁ at aneleventh exchange step ES₁₁ after lapse of the second predeterminedduration T₂. Thereafter, the central control unit 21 registers absenceof the first person A in the specific address for the firstidentification number ID₁ at a twelfth exchange step ES₁₂.

After registration of absence, the twelfth exchange step ES₁₂ isfollowed by the second exchange step ES₂ mentioned before.

It is readily understood from the above that the line number LN₁₀ forthe telephone set T₁₀ is memorized in the specific address assigned tothe first identification number ID₁ as long as the specific person A ispresent in the first zone Z₁.

Let the first person A leave his seat and meet another person C in thesecond zone Z₂ to make arrangements with him. In this event, the radiosignal generated by the first radio transmitter TX₁ can not be receivedby the first radio receiver RX₁ because it is very weak in intensity asmentioned before when the first person A arrives at the seat of anotherperson C. Instead, the second radio receiver TX₂ in the second zone Z₂receives the radio signal of the first radio transmitter TX₁. Inasmuchas the second radio receiver TX₂ and the telephone set T₂₀ are connectedto the subscriber line L₂₀ in common, the first identification numberID₁ is sent through the subscriber line L₂₀ to the exchange 11. When thefirst identification number ID₁ is detected from the radio signal twiceor more in the manner illustrated in conjunction with FIG. 4, theidentification memory area 27 is renewed from the line number LN₁₀ intothe line number LN₂₀ at the specific address assigned to the firstidentification number ID₁.

This means that a terminating call for the first person A is transferredto the telephone set T₂₀ placed at the seat of the second person D whilethe first person A is staying in the second zone Z₂. In other words, theterminating call for the first person A is not transferred to thetelephone set T₂₁ placed at the seat of the person C talking with thefirst person A. However, no problem might occur because each zone isvery narrow.

Thus, the identification memory area 27 is successively andautomatically renewed at the specific address assigned to the firstidentification number ID₁ as the first person A moves in the limitedarea. Similar operation is carried out as regards the second and thethird persons D and E.

From the above, it is readily understood that the identification memoryarea 27 is renewed only when each specific person changes the zones fromone to another. Accordingly, it is possible to prevent the subscriberlines, such as L₁₀, L₂₀, and L₃₀, from being occupied by the radioreceivers for a long time. Consequently, usual communication is alsocarried out through the subscriber lines L₁₀, L₂₀, and L₃₀.

Referring to FIG. 5 afresh and FIGS. 1 and 3 again, operation of thecentral control unit 21 will be described on the assumption that theexchange 11 receives a terminating call through one of the subscriberlines L and the external lines EXT, as shown at a first processing stepPS₁ in FIG. 5. The terminating call is accompanied either by a directorynumber TEL or by a person identification number ID. If the directorynumber TEL is detected at a second processing step PS₂, the centralcontrol unit 21 rings one of the telephone sets that is indicated by thedirectory number TEL, as shown at a third processing step PS₃.

If the terminating call carries the person identification number ID, thecentral control unit 21 accesses the identification memory area 27 at afourth processing step PS₄ to detect contents of an address assigned tothe person identification number ID at a fifth processing step PS₅. Whenthe contents of the address in question are indicative of the fact thatthe person for the person identification number ID is in course ofmoving, as illustrated at the ninth exchange step ES₉, the centralcontrol unit 21 energizes the first talkie unit TK₁ (FIG. 3) at a sixthprocessing step PS₆. The first talkie unit TK₁ gives information upon ashort absence in the form of an audio signal.

Unless the person under consideration is in course of movement, thefifth processing step PS₅ is followed by a seventh processing step PS₇at which the central processing unit 21 judges whether or not he isabsent from the limited area. When absence of the person is registeredin the manner illustrated in conjunction with the twelfth exchange stepES₁₂ of FIG. 4, the second talkie unit TK₂ is energized to giveinformation upon a long absence of the person assigned with the personidentification number ID in question at an eighth processing step PS₈.Otherwise, the seventh processing step PS₇ is succeeded by a ninthprocessing step PS₉ at which the line number LN is detected from thecontents of the address for the person identification number ID.

The central control unit 21 judges at a tenth processing step PS₁₀whether or not the subscriber line L specified by the line number LN isput into a busy state. Unless the subscriber line LN is busy, thecentral control unit 21 rings one of the telephone sets that is placedin a destination one of the zones Z and is connected to the subscriberline LN in the destination zone, as shown at an eleventh processing stepPS₁₁.

In the example being illustrated, the telephone sets in the destinationzone are successively searched to detect an idle one of the telephonesets in the order of priority predetermined in the destination zone whenone of the telephone sets in the destination zone is put into a busystate. For this purpose, the central control unit 21 matches states ofthe subscriber lines L included in the destination zone in the order ofthe priority. For example, judgement is made at a twelfth processingstep PS₁₂ to indicate whether or not the subscriber line of secondpriority is busy. Similarly, judgement is made as regards the subscriberline of third priority at a thirteenth processing step PS₁₃.

At any rate, one of the telephone sets is rung in the destination zoneat the eleventh processing step PS₁₁, if an idle one of the subscriberlines L is found out. Thus, a destination of each specific person isautomatically sought by the central control unit 21 with reference toeach person identification number ID to ring a neighboring one of thetelephone sets through the switch unit 22. When all of the subscriberlines L are regarded as busy at a fourteenth processing step PS₁₄, abusy tone is produced as shown at a fifteenth processing step PS₁₅.Thus, a combination of the central control unit 21 and the switch unit22 serves to transfer the terminating call and may be called a calltransfer member.

From the above, it is readily understood that the above-mentioned calltransfer is carried out only when one of the person identificationnumbers ID is given to the exchange 11. If a particular one of personsis informed of the one of the person identification numbers assigned toa specific person and calls the specific person by the use of the oneperson identification number only in case of emergency, an emergent callalone is favorably transferred to the specific person. In addition, thecall transfer is carried out without any manual operation.

Referring to FIGS. 6, 7, and 8, an automatic call transfer systemaccording to a second embodiment of this invention carries out automaticcall transfer by the use of first through n-th burst successions asillustrated along top through bottom lines TX₁ to TX_(n) of FIG. 6. Moreparticularly, each burst succession has a pair of bursts each of whichcarries a person identification number assigned to each specific person.The bursts of each pair consist of a leading and a trailing one.

The illustrated leading bursts of each burst succession are repeated ata period peculiar to the burst succession, like the burst successionsillustrated in FIG. 2. Therefore, the first burst succession illustratedalong the top line TX₁ of FIG. 6 includes the leading bursts appearingin the first period t₁ as shown in FIG. 2. Likewise, the second throughn-th burst successions TX₂ to TX_(n) include the leading bursts havingthe second through n-th periods t₂ to t_(n), respectively.

The leading bursts of each burst succession are followed by the trailingbursts spaced apart from the leading ones with a time interval Δt₁, Δt₂,. . . , or Δt_(n) left therebetween. The time intervals Δt₁ throughΔt_(n) are inherent to the burst successions TX₁ to TX_(n),respectively, and shorter than the periods, respectively. Thus, eachburst succession has the period, such as t₁, t₂, . . . , or t_(n), andthe time interval, such as Δt₁, Δt₂, . . . , or Δt_(n), peculiarthereto.

Let the leading bursts of the first through n-th burst successionshappen to appear in a single zone simultaneously with one another at atime instant t₀ in FIG. 6. In this event, the radio receiver RX can notdistinguish the person identification numbers ID from one another.However, the radio receiver can receive each person identificationnumber twice after both of each time interval Δt (suffixes omitted) andeach period t. The person identification numbers are therefore rapidlydetected twice or more from each burst succession in comparison with theburst successions illustrated in FIG. 2.

In FIG. 7, each radio transmitter TX comprises first and second timers36 and 37 for measuring each period t and each time interval Δt both ofwhich are peculiar to the burst succession, respectively. The first andsecond timers 36 and 37 are always energized by a battery 39 to producea succession of first pulses P₁ at each period t and a succession ofsecond pulses P₂ appearing when each time interval Δt lapses after thefirst pulses P₁. The first and the second pulses P₁ and P₂ last duringthe bursts.

A switch 41 is closed during presence of the first and the second pulsesP₁ and P₂ to intermittently connect the battery 39 to an identificationsignal circuit 43. The identification signal circuit 43 comprises anidentification (ID) number generator 45, a modulator 46, and anamplifier 47, which are all simultaneously energized by the battery 39.The person identification number is intermittently generated by theidentification number generator 45 and is subjected to modulation andamplification by the modulator 46 and the amplifier 47 to be produced asa radio signal through an antenna 48.

The radio signal is received by a radio receiver RX illustrated in FIG.8 and is sent through a reception antenna 51 to a decoding circuit 52 tobe decoded into a decoded signal representative of the personidentification number ID. The decoded signal is memorized in anidentification number memory 53 and is counted by a counter 54 which iscounted up at every reception of the decoded signal. When the samedecoded signal is received twice or more, the identification numbermemory 53 sends the decoded signal through a sender 56 and a selector 57to one of the subscriber lines indicated at L_(a1), L_(a2), . . . , andL_(am).

A busy detector 59 is coupled to the sender 56 and the selector 57. Thebusy detector 59 successively searches the subscriber lines L_(a1) toL_(am) to detect an idle one of the subscriber lines L_(a1) to L_(am).On detection of the idle subscriber line, the busy detector 59 connectsthe selector 57 to the idle subscriber line. As a result, the decodedsignal carrying the person identification number is sent through theidle subscriber line to the exchange 11. The illustrated radio receiverRX is assigned with a plurality of the subscriber lines L_(a1) toL_(am).

As mentioned before, the terminating call is automatically transferredto each of the specific persons given the person identification numberseven when each specific person frequently changes a destination from oneto another in the limited area and even when each specific personforgets to inform of change of the destination. In addition, theabove-mentioned call transfer can be individually carried out about eachof persons to which a single telephone is dispensed, when the differentperson identification numbers are assigned to the respective persons.

The periods t₁ through t_(n) of the bursts may be decided inconsideration of the number of the specific persons, areas of the zones,and electric power of the radio transmitters. Preferably, the periods tare longer than a time necessary for passing through each zone. Anyway,production of the bursts results in a reduction of electric powerconsumption in each radio transmitter TX.

In addition, each of the radio receivers may convert the personidentification number ID into an electric signal of a frequency bandhigher than an audio frequency band. The electric signal may thereafterbe subjected to demodulation by the exchange 11 to be rendered into theaudio frequency band. Instead of searching an idle of the subscriberlines, an offering connection may be made to preferentially carry outcall transfer on reception of a terminating call when a subscriber linein question is busy.

While this invention has thus far been described in conjunction with afew embodiments thereof, it will readily be possible for those skilledin the art to put this invention into practice in various other manners.For example, each radio receiver may directly transfer the receivedperson identification numbers ID to the exchange 11 without passingthrough the identification memory 53 as illustrated in FIG. 8. In thisevent, the central control unit 21 should carry out operations asillustrated at the second through seventh receiver steps RS₂ to RS₇(FIG. 4) instead of the radio receivers RX, although the subscriberlines L₁₀, L₂₀, and L₃₀ may be occupied by the radio receivers RX for along time. The radio receivers RX may not always be connected inparallel to the telephone sets, such as T₁₀, T₂₀, and T₃₀, but may beconnected through exclusive lines. The bursts illustrated in FIGS. 2 and6 may be variable in their periods and time intervals to avoidconcurrent occurrence of the bursts. In lieu of the bursts, the personidentification numbers ID may be produced in a frequency divisionfashion when the exchange 11 has a comparatively small capacity and maybe continuously produced by each radio transmitter. The exchange may notbe a private branch exchange. When the receivable zones Z₁, Z₂, and Z₃are partially intersected to one another, each person identificationnumber may be received by a plurality of the radio receivers RX. If anintersected portion includes the home zone, the person identificationnumber may be registered in the home zone in preference to the otherzone or zones. If no home zone is included in the intersected portion,the person identification number may be registered in one of thereceivable zones that receives a new one of the person identificationnumbers. The receivable zones may not always cover the whole of thelimited area because the short absence can be indicated in theillustrated system.

Furthermore, ultrasonic waves may be used to couple the transmitters TXto the receivers RX instead of the radio signals. An inductive radiomethod may be used to couple the transmitters TX and the receivers RX.

In any event, no manual operation is necessary to register each linenumber of the destination zone because each line numbers is successivelyand automatically memorized and renewed in the identification memoryarea 27.

What is claimed is:
 1. In an automatic call transfer system for use inautomatically carrying out transfer of a call by the use of an exchangewhich is coupled through subscriber lines to telephone sets,respectively, said telephone sets being specified by line numberscorresponding to said subscriber lines, respectively, and beingdistributed in an area so as to be utilized by persons movable in saidarea, the improvement wherein:a person identification number is assignedto each of specific ones of said persons so as to identify said eachspecific person; said system comprising: a plurality of receiving meanscoupled to said exchange and having receivable zones into which saidarea is divided so that at least one of said telephone sets is includedin each of said receivable zones, each of said receiving means being forreceiving an identification number signal representative of said personidentification number; and signal generating means conveyed by said eachspecific person for generating said identification number signal suchthat it is received by a selected one of said receiving means when saideach specific person is staying in the receivable zone for said selectedone of said receiving means; said exchange comprising: memory meanscoupled to said receivers for memorizing specific at least one of theline numbers of the receivable zone for said selected one of saidreceiving means in correspondence to said identification number signal;and call transferring means coupled to said memory means and responsiveto the call carrying said person identification number for transferringthe call to the telephone set specified by said specific at least one ofsaid line numbers with reference to the memorized identification numbersignal.
 2. An automatic call transfer system as claimed in claim 1,wherein said signal generating means produces said identification numbersignal in the form of a radio signal while each of said receiversproduces an electric identification signal representative of said personidentification number in response to said radio signal.
 3. An automaticcall transfer system as claimed in claim 2, wherein said signalgenerating means comprises:burst producing means for producing asuccession of bursts each of which carries said identification numbersignal and has a predetermined period peculiar to said personidentification number; and means for producing said succession as saidradio signal.
 4. An automatic call transfer system as claimed in claim2, wherein said signal generating means comprises:burst pair producingmeans for repeatedly producing a pair of bursts each of which carriessaid person identification number, said bursts of each pair appearingwith a burst interval left therebetween and being specific to saidperson identification number; and means for producing said pair ofbursts as said radio signal.
 5. An automatic call transfer system asclaimed in claim 2, wherein each of said receiving means comprises:localmemory means for memorizing said electric identification signal; andsending means for sending said memorized electric identification signalto said exchange only on occurrence of variation of the personidentification number conveyed by said radio signal.
 6. An automaticcall transfer system as claimed in claim 5, wherein each of saidreceiving means further comprises:monitoring means coupled to saidsending means and the subscriber lines for each receivable zone formonitoring the subscriber lines to detect an idle one of the subscriberlines and to deliver said memorized electric identification signal tosaid idle subscriber line.
 7. An automatic call transfer system asclaimed in claim 1, wherein said signal generating means is coupled toeach of said receivers by the use of ultrasonic waves.